In the field of coal liquefaction, for example, attempts have been made to convert a coal to a liquefied oil through hydrocracking, and research and development works have been enthusiastically conducted since the achievement of the Bergius process. Many coal liquefaction processes have been proposed so far, including the new IG process, H-Coal process, SRC-II process and EDS process.
In coal liquefaction processes using catalysts, some catalysts are used by the ebullition bed method with liquefaction reactor, and others are used by being added to coal slurries. Known as a representative of the former are particulate catalysts comprising nickel, cobalt, molybdenum or the like supported on a support such as alumina. Known as a representative of the latter catalysts are powdery iron compounds such as iron oxide, iron ore, and red mud.
However, the former and the latter catalysts have unsolved problems mainly from the standpoints of catalyst deterioration and catalytic activity, respectively.
Recently, proposals have come to be made on techniques for efficiently conducting coal liquefaction in the method in which a catalyst is added to a coal slurry. These techniques comprise employing a catalyst having an increased functional-ingredient content, or comprise employing a catalyst having a reduced particle size so as to finely disperse the catalyst, each to thereby heighten the efficiency of the contact thereof with the coal and solvent. With respect to the case in which iron ore, iron hydroxide, red mud, iron sulfate or the like is used, it has been proposed to conduct the liquefaction reaction in the presence of sulfur to thereby greatly enhance the liquefaction activity. Naturally occurring pyrite is also well known to have catalytic activity. A process for chemically synthesizing a pyrite in order to heighten the content of FeS.sub.2, serving as an active ingredient, is described, e.g., in Unexamined Published Japanese Patent Application No. 59-183831, which comprises using ferrous sulfate heptahydrate, sodium sulfide, and solid sulfur as starting materials to synthesize iron disulfide by a wet method. In this process, the iron disulfide yielded is taken out of the aqueous solution by filtration, washed, and the subjected to drying and pulverization steps.
Examined Japanese Patent Publication No. 61-60115 and Unexamined Published Japanese Patent Application No. 5-98266 proposed simplified processes in which ferrous sulfate is reacted as a starting material with hydrogen sulfide and elemental sulfur, respectively, as a sulfurizing agent at a high temperature by a dry method. A similar dry process is proposed in Unexamined Published Japanese Patent Application No. 61-268357, in which process the crystal water and adherent water of ferrous sulfate for use as a starting material are treated by drying, followed by burning at a high temperature with hydrogen sulfide and elemental sulfur.
However, the catalysts proposed so far are unsatisfactory in liquefaction yield when used in a system in which iron ore, iron hydroxide, red mud, iron sulfate or the like coexists with sulfur. Furthermore, it is known that use of prior art catalysts causes the deposition of a scale comprising mainly of iron compounds, on the inner surface of the tube of a preheater in a liquefaction plant, to thereby plug the flow path to arouse troubles in continuous operation. There also is a currently employed technique in which pyrite as a starting material is pulverized with a small-diameter ball mill or the like. However, since pyrite has a Mohs' hardness of 6 or higher, the balls or the main pulverizer body (rotor and stator) suffers considerable wear and should be replaced more frequently. Consequently, the particle size reduction of pyrite is limited, and the catalyst obtained cannot have a large surface area, resulting in a low liquefaction yield.
The catalyst synthesized by the wet process described above has drawbacks that the second step reaction, i.e., reaction between FeS and sulfur, takes much time because it is a solid-phase reaction, and that the catalyst contains ingredients other than iron disulfide, e.g., unreacted sulfur and Glauber's salt. Namely, this catalyst is still insufficient from the standpoints of hydrogenation activity and practical catalyst production, and is insufficient also in liquefaction efficiency.
The ferrous sulfate used as a starting material in the dry process disclosed in Examined Japanese Patent Publication No. 61-60115 is a 325-mesh pass (46 .mu.m or smaller), while that used in Unexamined Published Japanese Patent Application No. 5-98266 has a particle diameter of from 8 to 15 .mu.m. In the case where a 20-.mu.m starting material, for example, is reacted in a fluidized burning furnace, the superficial velocity should be reduced to the 0.01 m/sec level for ensuring an in-furnace residence time necessary for obtaining a sufficient conversion. In industrial apparatuses, part of a sulfurizing agent is burned with air in order to supply heat of reaction. However, since the amount of air that can be introduced at such a low flow rate is limited, the result is either a reduced production rate or the necessity of heating from the outer wall of the furnace. If the superficial velocity is increased, for example, to 0.1 m/sec so as to increase productivity in the reaction of ferrous sulfate particles having a diameter in the above range, it is thought that the density of the fluidized bed decreases and the proportion of particles which go out through the furnace overhead nozzle (short-residence-time particles) increases, resulting in a reduced conversion and impaired suitability for disaggregation of product particles.
There is a strong desire for the economical production of a catalyst substance which has high liquefaction activity and is reduced in scale deposition in a preheater in a liquefaction plant, that is, which has a high FeS.sub.2 content and a low content of non-catalytic components other than iron compounds and is capable of being dispersed as submicron particles having a sufficient surface area when used in coal liquefaction or in the hydrocracking reaction of a heavy oil.
The present invention has been achieved in order to provide an iron sulfide which exhibits excellent catalytic activity in hydrogenation when used in coal liquefaction or in the hydrocracking reaction of a heavy oil, and to provide an efficient process for producing the same. Because of the excellent catalytic activity in hydrogenation, it is possible to attain a high conversion of coal, a high yield of liquid, a high yield of light oil, and improvements in the quality of liquefied oil, such as a reduced content of hetero-compounds, even when the catalyst is used in a discardable small amount.